1. Technical Field of the Invention
The present invention relates to a telecommunications network and, in particular, to the conversion of a routing address within a Signaling System No. 7 (SS7) signal.
2. Description of Related Art
Whenever a mobile station travels into a new Mobile Switching Center (MSC) coverage area or turns on its unit for the first time, the mobile station attempts to register with the serving MSC by transmitting an associated identification number known as the International Mobile Subscriber Identity (IMSI) number to the serving MSC. The serving MSC then communicates with the particular home location register (HLR) which stores subscriber information associated with the mobile station to inform the HLR of the mobile station's new location and to retrieve the requisite subscriber information from the HLR. Accordingly, the serving MSC, the HLR, and the connecting telecommunications network must have a mechanism for communicating signals between the serving MSC and the HLR. For example, North America and Europe each has its own particular addressing mechanism for communicating a signal between a particular MSC and an HLR within its own Signaling System No. 7 (SS7) network. However, there exist certain differences between these two addressing mechanisms which prevent an MSC located within one SS7 network to communicate with an HLR located within the other SS7 network.
North America currently follows the E.212 based addressing mechanism whereas Europe follows the E.214 based addressing mechanism. E.212 and E.214 are address formats and syntax enunciated by the International Telecommunication Union (ITU) for routing signals and data within a particular SS7 telecommunications network. One example of a system based on the E.212 addressing mechanism in the United States is the Personal Communications System (PCS) 1900 telecommunications network. On the other hand, an example of a system based on the E.214 addressing mechanism in Europe is the Global System for Mobile (GSM) telecommunications network. The PCS network uses the received IMSI number (E.212) from the mobile station to route a signal to an HLR within the North American Signaling System No. 7 (SS7) telecommunications network. In contrast, the GSM system modifies the received IMSI number to another number called Mobile Global Title (MGT, E.214) and uses the MGT number to route a signal to an HLR within the European SS7 telecommunications network.
Because one SS7 network does not contain translation data for handling the address number specified by the other SS7 network, the North America SS7 telecommunications network cannot currently route signals using the MGT number and the European SS7 telecommunications network similarly cannot route signals using the IMSI number. Consequently, when a mobile station associated with a United States service provider roams into an European country, there exists an incompatibility from a network signaling stand point. The serving MSC associated with the European SS7 telecommunications network cannot communicate a Mobile Application Part (MAP) based signal with the HLR located within the United States. Without performing the location update procedure, the HLR does not know where the mobile station is currently located and the serving MSC is not provided with the requisite subscriber information (e.g., billing information) for providing the requested mobile service to the roaming mobile station.
A number of proposals have been introduced to solve the above addressing incompatibility existing between the PCS and the GSM systems. One such proposal suggests changing the European SS7 telecommunications network to also route signals using the IMSI (E.212) number. Even though this proposal would establish global compatibility, all associated signal transfer points (STPs) and signal handling nodes within the European SS7 telecommunications network have to be modified at great costs and effort. Even if all the European countries could agree to make such modifications, this would be an enormous undertaking.
Accordingly, there is a need for a mechanism to enable the routing of MAP based signals from the European SS7 telecommunications network to the North American SS7 telecommunications network without mandating major changes or impacts on the existing networks.